Impact of Hydroponically Grown Fruits and Vegetables on Bioactive Compounds Found Within

Desert/steppe environments characterize the Great Basin, where dry air masses induce broad ranges in daily temperature throughout the seasons and increase the probability of killing frosts at the beginning and end of growing seasons. Consequently, Nevada’s major agricultural enterprises include forage (largely alfalfa), livestock and some dairy, i.e. agricultural products that are less sensitive to daily and seasonal temperature variations.

Although water resources are limited, the abundance of clear, cloudless days (estimated to be as much as 90% of days in typical year) provide copious sunlight and energy for plant growth. Therefore, with the appropriate tools such as greenhouses, hoop houses, hydroponics, and linkages to alternative energy resources, sustainable agricultural production of specialty crops can be developed in northern Nevada.

The objective of this project is to improve fruit and vegetable production through research, education, and outreach utilizing hoop houses, greenhouses and hydroponics. The project is a joint venture between two UNR colleges, nonprofit firms, schools, food services and several restaurants located in northern Nevada.

Hydroponic growers are becoming more widespread throughout the United States and worldwide. Of the estimated 50,000 acres in hydroponic production around the world, about 1200 (less than 3%) are in the U.S. Most of the hydroponic facilities in the U.S. are small (<1 acre), family or small business operations that produce premium hydroponic produce for sale locally. The smaller operations usually have the advantage of offering vine-ripened, locally grown produce with minimal transportation cost and spoilage and shipping losses (Jensen and Collins, 1985).

Several large hydroponic facilities in the U.S. cover > 60 acres and produce large quantities of hydroponic tomatoes, peppers, cucumbers and lettuce. Bell Horticultural, a U.S. ornamental plant cuttings and seed production company, recently announced that it would develop a $15 million, 97.4 acres hydroponic project in Nicaragua (Brennon, 2011).

Often hydroponic growers use greenhouses or less expensive hoop houses to aid them in expanding the ability for continuous production in areas with short growing seasons. Hoop houses have gained recent notice in the United States with placement on the White House grounds and support from the USDA’s Deputy Secretary Kathleen Merrigan, who announced a three-year study on hoop house effectiveness in December 2009.

In northern Nevada, food production is limited by the cold arid climate. To mitigate risk associated with early and late season weather variability, especially frosts, the Natural Resource Conservation Services and Specialty Crops Institute of Western Nevada Community College have supported construction of hoop houses, which are simple structures designed to trap insolation to maintain internal soil and air temperatures at levels sufficient to support plant production.

Lattin Farms, a very successful community supported agricultural enterprise based in the northern Nevada town of Fallon, has constructed hoop houses in the Lahontan Valley.

In the past year, 130 farmers and community members attended a hoop house building workshop held by Western Nevada College’s Specialty Crop Institute. Community and backyard gardening are also very popular, supported by the Master Gardener program of University of Nevada College of Cooperative Extension and the Grow Your Own Nevada program. The City of Reno Department of Parks, Recreation and Community Services’ program has established “Tegilia’s Paradise Park Community Garden,” and other groups, such as Urban Roots, Edible Reno-Tahoe, the River School, Hungry Mother Farms and FOCUS (For Our County, United States – a therapeutic outreach program for combat veterans) are part of a growing and enthusiastic network of small-scale food producers in northern Nevada.

Fresh vegetables and fruits are sources of bioactive nutrients with significant health benefits. Bioactive nutrients can be defined as food constituents that have beneficial health effects. This definition includes essential nutrients that, when consumed at a rate that exceeds the minimum recommended intake per day, has been shown to have health benefits.

The bioactive nutrient content of vegetables is influenced by several key factors including genotype selection and environmental conditions (light, temperature, humidity, atmospheric CO2, and presence of pollutants in the air) (Thybo et al., 2005). Over time and through genotype selection, hybrid cultivars have been developed with high yield potential, uniform and pleasing appearance, and disease tolerance.

Because of increased consumer interest, the content of health promoting compounds is becoming a vital consideration for fruit and vegetable growers. Plant-breeding programs have enhanced levels of carotenoids (Ronen et al., 2000) and other antioxidants (Schijlen et al., 2004).

Nutritional quality of vegetables also can be manipulated by changes in light and water stress. For example:

growing stresses can be manipulated to increase levels of anthocynanins, which enhance the purple-fruitiness of tomatoes (Jones et al., 2003).

Higher altitudes increase visible and UV light, which in turn increase plant carotenoid contents, a function of absorbed light during photosynthesis and the need to protect the plant from excessive light.

Vitamin C is synthesized from sugars, and the amount and intensity of light during the growing season affects sugar synthesized via photosynthesis (Lee and Kader 2000).

For other bioactive compounds, light of sufficient energy is important to promote the photosynthetic production of carbohydrates, which in turn are the substrates for flavonoid biosynthesis via the shikimic acid and phenylpropanoid pathways.

In arid and urban environments, quality and quantity of water is a prominent factor for agricultural ventures. Water resources, including treated water delivered by public water supply providers, can have high concentrations of total dissolved solids.

For example, water produced by the Truckee Meadows Water Authority is considered slightly hard, with a concentration of dissolved constituents ranging from 30-35 mg/l in areas with water supplies derived primarily from snowmelt.

Given the high potential evaporation rates in the Great Basin, these solids can accumulate in the soil with the resulting increase in soil salinity. This can lead to crop failure or damage. It may also require the use of leaching strategies, with attendant problems of leaching water disposal.

Because water sources for hydroponics in urban areas also rely on domestic water providers, accumulation of solids and salts may be especially problematic because nutrient solutions are constantly recycled in hydroponic systems, which will require research to develop appropriate means to maintain growth.

We anticipate that laboratory analysis of nutrient and bioactive compound content of hydroponically grown crops will meet or exceed those grown or obtained from traditional techniques. These studies will aid us in evaluating environmental effects (stress and water) on maximizing production of selected nutrients and bioactive compounds in fruits and vegetables grown hydroponically or in soil.

The objective of this research and extension proposal is to assess the quality of nutrient and bioactive compounds and water efficiency in crops grown hydroponically using low cost season extension structures that are becoming increasingly common in the region (hoop houses).

Our goal is to demonstrate that hydroponics coupled with hoop houses can produce a sustainable supply of fruits and vegetable for communities in northern Nevada. Specific objectives include:

Renovate two hoop houses for vegetable and fruit research, one using soil in raised plant beds and the other using hydroponic technology.

Evaluate the interactions among production of selective bioactive compounds, sensory quality, and plant growing conditions (including plant stress and water quality and utilization).

Build upon a successful UNCE program (Grow your own Nevada) to provide outreach/educational opportunities for commercial growers and for educational, non-commercial growers in northern Nevada schools.

Establish a partnership with the emerging local food 2 network and food service entities for sustainable production/distribution of fruits and vegetables grown in hoop houses using hydroponics.

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